Chemistry
Types of Lipids
Lipids are diverse molecules that are insoluble in water. The main types of lipids include triglycerides, phospholipids, and sterols. Triglycerides are the most common type and serve as a major form of energy storage. Phospholipids are essential components of cell membranes, while sterols, such as cholesterol, play important roles in cell structure and as precursors for hormones.
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10 Key excerpts on "Types of Lipids"
eBook - PDF- H. Stephen Stoker(Author)
- 2015(Publication Date)
- Cengage Learning EMEA(Publisher)
Prior to discussing additional types of lipid molecules—emulsification lipids (Section 8-11), messenger lipids (Sections 8-12 and 8-13), and protective-coating lipids (Sec-tion 8-14)—the discussion of membrane lipids will be extended to include how these Types of Lipids interact with each other to form cell membranes. ◀ Living cells contain an estimated 10,000 different kinds of molecules in an aqueous environment confined by a cell membrane. A cell membrane is a lipid-based structure that separates a cell’s aqueous-based interior from the aqueous environment 1. The “steroid nucleus” common to all steroid structures involves a fused-ring system that contains a. four 6-membered rings b. four 5-membered rings c. three 6-membered rings and one 5-membered ring d. no correct response 2. Which of the following types of membrane lipids has a steroid structure? a. cholesterol b. sphingoglycolipids c. sphingophospholipids d. no correct response 3. Which of the following statements concerning cholesterol is correct ? a. An alcohol functional group is present in its structure. b. The lipoprotein HDL distributes cholesterol to various parts of the human body. c. The cholesterol associated with LDL is often called “good cholesterol.” d. no correct response Section 8-9 Quick Quiz Answers: 1. c; 2. a; 3. a ▶ Cell membranes are also com-monly called plasma membranes because they separate the cyto-plasm (aqueous contents) of a cell from its surroundings. Copyright 2016 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.
eBook - PDF- Khetarpaul, Neelam(Authors)
- 2021(Publication Date)
- Daya Publishing House(Publisher)
Chapter 1 Definition and Classification of Lipids I Definitions of Lipid Lipids come from the Greek lipos, meaning fat. Although lipid analysts tend to have a firm understanding of what is meant by the term “lipid”, there is no widely-accepted definition. Fats and oils are classified as “lipids” which is a category that embraces a broad variety of chemical substances. In addition to triglycerides, it also includes monoand diglycerides, phosphatides, cerebrosides, sterols, terpenes, fatty alcohols, fatty acids, fat-soluble vitamins, and other substances. Generally, lipids are usually described as a group of naturally occurring compounds, which are hydrophobic and have in common a ready solubility in such organic solvents as hydrocarbons, chloroform, benzene, ethers and alcohols. They include a diverse range of compounds, like fatty acids and their derivatives, carotenoids, terpenes, phospholipids, steroids, bile acids and waxes. It should be apparent that many of these compounds have little by way of structure or function to relate them. In fact, a definition of this kind is positively misleading, since many of the substances that are now widely regarded as lipids may be almost as soluble in water as in organic solvents. Lipids are fatty acids and their derivatives, and substances related biosynthetically or functionally to these compounds. This treats cholesterol (and plant sterols) as a lipid, and could be interpreted to include bile acids, tocopherols and certain other compounds. It also enables classification of such compounds as gangliosides as lipids, although they are more soluble in water than in organic solvents. However, it does not include such natural substances as steroidal hormones, petroleum This ebook is exclusively for this university only. Cannot be resold/distributed. products, some fat-soluble vitamins, carotenoids or terpenes, except in rare circumstances. If “lipids” are defined in this way, fatty acids must be defined also.
- Morris Hein, Scott Pattison, Susan Arena, Leo R. Best(Authors)
- 2014(Publication Date)
- Wiley(Publisher)
The hydrophobic nature of lipids contributes significantly to the biological functions of these molecules. Their water insolubility allows lipids to serve as barriers to aqueous solu- tions. This property, as we shall see later, is of great importance when lipids form cellular membranes. Lipids are hydrophobic molecules; their structures are relatively large and nonpolar. Yet, within this broad description, lipid structures vary markedly. The following classification scheme recognizes important structural differences: 1. Simple lipids (a) Fats and oils: esters of fatty acids and glycerol. (b) Waxes: esters of high-molar-mass fatty acids and high-molar-mass alcohols. 2. Compound lipids (a) Phospholipids: substances that yield glycerol, phosphoric acid, fatty acids, and a nitrogen-containing base upon hydrolysis. (b) Sphingolipids: substances that yield an unsaturated amino alcohol (sphingosine), a long-chain fatty acid, and either a carbohydrate or phosphate and a nitrogen base upon hydrolysis. (c) Glycolipids: substances that yield sphingosine, a fatty acid, and a carbohydrate upon hydrolysis. 3. Steroids Substances that possess the steroid nucleus, which is a 17-carbon structure consisting of four fused carbocyclic rings. Cholesterol and several hormones are in this class. 4. Miscellaneous lipids Substances that do not fit into the preceding classifications; these include the fat-soluble vitamins A, D, E, and K, and lipoproteins. KEY TERM lipids An ester is formed by splitting out a molecule of water between an alcohol and an acid. LEARNING OBJECTIVE 28.2 • Simple Lipids 733 The most abundant lipids are the fats and oils. These substances constitute one of the three important classes of foods. In the discussion that follows, we examine fats and oils as they pertain to biochemistry. A more complete consideration of the properties and composition of various fats and oils is given in Section 24.9.
eBook - PDF- Jose Perez-Castineira(Author)
- 2020(Publication Date)
- De Gruyter(Publisher)
4 Lipids 4.1 Definition and classification Lipids are a heterogeneous family of biomolecules whose common characteristic is a low or null solubility in water and high solubility in non-polar organic solvents such as chloroform or hexane. This definition includes a wide variety of biological com- pounds that can be classified according to different criteria, such as behavior upon hydrolyzation or chemical structure and composition [1]. According to the first crite- rion, lipids are classified as: – Hydrolysable (saponifiable) lipids. Those that yield fatty acids when subjected to hydrolysis in the presence of strong acids (soaps in the presence of strong bases such as NaOH or KOH). – Non-hydrolysable (unsaponifiable) lipids. They do not produce fatty acids/soaps upon hydrolysis. Considering chemical structure and composition, food chemists distinguish three clas- ses of lipids: – Simple lipids: esters of fatty acids and biological alcohols like glycerol (propane- 1,2,3-triol). This group is of paramount importance due to their abundance in foods, as they include fats and oils. – Compound, complex, or conjugated lipids: lipids linked or associated to other non-lipid molecules producing substances with amphiphilic properties. These include phospholipids, glycolipids, and lipoproteins. – Derived lipids. Hydrophobic substances not included in the above groups, such as free fatty acids, carotenoids, lipophilic vitamins, steroids, or pigments and volatile scents from plants. Similarly to the rest of biomolecules, the backbones of lipids are composed mainly of carbon, hydrogen, and oxygen although they may contain additional elements such as phosphorus, sulfur, and/or nitrogen. Lipids are molecules of hydrophobic nature implicated in important biological functions: – Energetic.
No longer available |Learn more- Sharon Rady Rolfes, Kathryn Pinna, Ellie Whitney(Authors)
- 2017(Publication Date)
- Cengage Learning EMEA(Publisher)
Fat refers to the class of nutrients known as lipids. The lipid family includes triglycerides (fats and oils), phospholipids, and sterols. Triglycerides are most abundant, both in foods and in the body. The following sections describe the similarities and differences among the remarkably diverse members of the lipid family. 1 5 The Lipids: Triglycerides, Phospholipids, and Sterols Copyright 2018 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-300 134 Chapter 5 5-1 The Chemist’s View of Fatty Acids and Triglycerides LEARN IT Recognize the chemistry of fatty acids and triglycerides and differ-ences between saturated and unsaturated fats. Like carbohydrates, lipids are composed of carbon (C), hydrogen (H), and oxygen (O). Because lipids have many more carbons and hydrogens in proportion to their oxygens, they can supply more energy per gram than carbohydrates can (Chapter 7 provides details). The many names and relationships in the lipid family can seem overwhelming— like meeting a friend’s extended family for the first time. To ease the introductions, this chapter first presents each of the lipids from a chemist’s point of view using both words and diagrams. Then the chapter follows the lipids through digestion and absorption and into the body to examine their roles in health and disease. For people who think more easily in words than in chemical symbols, this preview of the upcoming chemistry may be helpful: 1. Every triglyceride contains one molecule of glycerol and three fatty acids (basically, chains of carbon atoms). 2. Fatty acids may be 4 to 24 (even numbers of) carbons long, the 18-carbon ones being the most common in foods and especially noteworthy in nutrition. 3. Fatty acids may be saturated or unsaturated. Unsaturated fatty acids may have one or more points of unsaturation—that is, they may be mono unsatu-rated or poly unsaturated.
eBook - PDFGeneral, Organic, and Biological Chemistry
An Integrated Approach
- Kenneth W. Raymond(Author)
- 2012(Publication Date)
- Wiley(Publisher)
1 Describe the structure of fatty acids and explain how saturated, monounsaturated, and polyunsatu- rated fatty acids differ from one another. 2 Identify the primary biological function of waxes and describe the esters that predominate in them. 3 Describe the makeup of triglycerides and list their biological functions. 4 Describe the structure of phospholipids and glycolipids. 5 Identify the basic steroid structure and list important members of this class of lipids. 6 Name the three types of eicosanoids and describe their biological function. 7 Describe the makeup of a cell membrane and explain how various compounds cross the membrane. 421 We have seen that molecules can be placed into families based on the functional groups that they possess—alkenes have a C “C group, alkynes a C ‚ C group, alcohols an iOH group, and so on. In this chapter we will consider the family of biochemical compounds called lipids. Compounds are not classified as lipids based on functional groups, but because they are largely water insoluble. Biologically, lipids are put to a wide range of uses, including as cell membrane components, as energy storage molecules, for insula- tion, and as hormones. As we will see, THG has a chemical structure similar to certain members of the class of lipids called steroid hormones. After completing this chapter, you should be able to: 11 L i pids and Membranes CHAPTER 11 OBJECTIVES ABOUT THIS CHAPTER 422 CHAPTER 11 Lipids and Membranes 11.1 FAT T Y A C I D S Fatty acids are the first class of lipids (water insoluble biochemical compounds) that we will consider. These are carboxylic acids that typically contain between 12 and 20 carbon atoms. When describing the structure of many lipids, the term head is used to represent a polar group and tail is used for a nonpolar hydrocarbon chain. In fatty acids, the head is the carboxyl group and the tail is the long chain of carbon atoms. Fatty acids typically have an even number of carbon atoms.
- Frederick Bettelheim, William Brown, Mary Campbell, Shawn Farrell(Authors)
- 2019(Publication Date)
- Cengage Learning EMEA(Publisher)
EXAMPLE 20.7 Cholesterol looks nothing like a fatty acid, triglycerol, or any of the other lipids presented up until this point. Why is it considered a lipid? STRATEGY You must find what is the same between cholesterol and all of the other lipid types discussed so far, eliminating those things that are different. SOLUTION Cholesterol would seem to have little in common with the other lipids. It does not have a fatty acid per se, as there is no carboxylic acid group. It does not have a glycerol or sphingosine backbone esterified to other fatty acids. Its structure of four fused rings looks nothing like the other lipids, yet it is a lipid. The only thing cholesterol has in common with the other lipids we have seen is that it is a nonpolar molecule. It has lots of carbons and very few atoms that are polar. It is a lipid based on the most basic definition of a lipid, molecules that are insoluble in water. ■ QUICK CHECK 20.7 Draw a picture of the steroid core and compare it to the structure of cho-lesterol. What parts do both molecules have? What parts are different? 20.11 Physiological Roles of Steroid Hormones Cholesterol is the starting material for the synthesis of steroid hormones. In a multi-step process, the aliphatic side chain on the D ring is shortened considerably and then hydroxylated. The hydroxyl group is oxidized giving an acetyl group attached at position 17 of the fused ring structure. The dou-ble bond is flipped so that it is between carbons 4 and 5, and the hydroxyl on carbon 3 is oxidized to a ketone group. The resulting molecule, proges-terone , serves as the starting compound for both the sex hormones and the adrenocorticoid hormones ( Figure 20.7 ). A. Adrenocorticoid Hormones The adrenocorticoid hormones (Figure 20.7) are products of the adrenal glands. The term adrenal means “adjacent to the renal” (which refers to the kidney).
eBook - PDFNutrition
Science and Applications
- Lori A. Smolin, Mary B. Grosvenor(Authors)
- 2016(Publication Date)
- Wiley(Publisher)
Some of the cholesterol in HDLs is taken directly to the liver for disposal, and some is transferred to organs that have a high requirement for cholesterol, such as those involved in steroid hormone synthesis (see Figure 5.11). High levels of HDL in the blood help prevent cholesterol from depositing in the artery walls and are associated with a reduction in heart disease risk. 5.5 Lipid Functions in the Body LEARNING OBJECTIVES • List four functions of lipids in the body. • Explain why enough of, and the right balance of, omega-3 and omega-6 fatty acids are needed in the diet. • Describe how fatty acids are used to generate ATP. • Discuss how fat is stored after a meal and how stored fat is retrieved between meals and during fasting. Lipids are necessary to maintain health. In our diet, fat is needed to absorb fat-soluble vitamins and is a source of essential fatty acids. In our bodies, lipids form structural and regulatory mol- ecules, are stored as an energy reserve, and are broken down via cellular respiration to provide energy in the form of ATP. Lipids Provide Structure and Lubrication Most of the lipids in the human body are triglycerides stored in adipose tissue, which is composed of adipocytes. Adipose tissue lies under the skin and around internal organs. Triglycerides in adi- pose tissue provide a lightweight energy storage molecule, cushion our internal organs, insulate the body from changes in temperature, and contribute to our body shape and contours (Figure 5.12). high-density lipoprotein (HDL) A lipoprotein that picks up cholesterol from cells and transports it to the liver so that it can be eliminated from the body. A high level of HDL decreases the risk of cardiovascular disease. adipose tissue Tissue found under the skin and around body organs that is composed of fat-storing cells. adipocyte A fat-storing cell. FIGURE 5.12 Adipose tissue A. The amount and location of adipose tissue affect our body size and shape.
eBook - PDFVisualizing Nutrition
Everyday Choices
- Mary B. Grosvenor, Lori A. Smolin(Authors)
- 2021(Publication Date)
- Wiley(Publisher)
3. Summarize how and when fatty acids are used to provide energy. 4. Describe how fat is stored and how it is retrieved from storage. Lipids are necessary to maintain health. In our diet, fat is needed to absorb fat-soluble vitamins and is a source of essen- tial fatty acids and energy. In our bodies, lipids form structural and regulatory molecules and are broken down to provide ATP. As discussed earlier, cholesterol plays both regulatory and structural roles: It is used to make steroid hormones, and it is an important component of cell membranes and the myelin coating that is necessary for brain and nerve function. Most lipids in the body are triglycerides stored in adipose tissue, which is body fat that lies under the skin and around internal organs (Figure 5.12). The triglycerides in our adipose tissue provide a lightweight energy storage molecule, help cushion our internal organs, and insulate us from changes in temperature. Triglycerides are also found in oils that lubricate body surfaces, keeping the skin soft and supple. Essential Fatty Acids Humans are not able to synthesize fatty acids that have dou- ble bonds in the omega-6 and omega-3 positions (see Fig- ure 5.4). Therefore, the fatty acids linoleic acid (omega-6) and alpha-linolenic acid (α-linolenic acid) (omega-3) are considered essential fatty acids. They must be consumed in the Large triglyceride droplet Nucleus and cytoplasm at the periphery of the cell Ed Reschke/Getty Images Karen KasmauskI/National Geographic Image Collection b. Adipose tissue cells contain large droplets of triglyceride that push the other cell components to the perimeter of the cell. As weight is gained, the triglyceride droplets enlarge. a. The amount and location of adipose tissue affect our body size and shape. When people have liposuction to slim their hips, the surgeon is actually vacuuming out fat cells from the adipose tissue in the region. FIGURE 5.12 Adipose tissue Adipose tissue is what we refer to as body fat.
eBook - PDFVisualizing Nutrition
Everyday Choices
- Mary B. Grosvenor, Lori A. Smolin(Authors)
- 2017(Publication Date)
- Wiley(Publisher)
Lipid Functions 125 This reverse cholesterol transport is accomplished by high- density lipoproteins (HDLs) (see Figure 5.11). HDL choles- terol is often called “good cholesterol” because high levels of HDL in the blood are associated with a reduction in the risk of heart disease. Concept Check 1. How does bile help in the digestion and absorption of lipids? 2. Why are lipoproteins needed to transport lipids? 3. What is the primary function of LDLs? 5.4 Lipid Functions LEARNING OBJECTIVES 1. List the functions of lipids in the body. 2. Explain why the ratio of omega-3 and omega-6 fatty acids is important in the diet. 3. Summarize how and when fatty acids are used to provide energy. 4. Describe how fat is stored and how it is retrieved from storage. Lipids are necessary to maintain health. In our diet, fat is needed to absorb fat-soluble vitamins and is a source of essential fatty acids and energy. In our bodies, lipids form structural and reg- ulatory molecules and are broken down to provide ATP. As dis- cussed earlier, cholesterol plays both regulatory and structural roles: It is used to make steroid hormones, and it is an import- ant component of cell membranes and the myelin coating that is necessary for brain and nerve function. Most lipids in the body are triglycerides stored in adipose tissue, which is body fat that lies under the skin and around internal organs (Figure 5.12). The triglycerides in our adipose tissue provide a lightweight energy storage molecule, help cushion our internal organs, and insulate us from changes in temperature. Triglycerides are also found in oils that lubricate body surfaces, keeping the skin soft and supple. Essential Fatty Acids Humans are not able to synthesize fatty acids that have dou- ble bonds in the omega-6 and omega-3 positions (see Fig- ure 5.4).
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